Cardiac function is typically assessed by measuring ejection fraction. This can be done using echocardiography or magnetic resonance (MR) imaging. However, it has been shown that myocardial strain is an early indicator of cardiac abnormality. The term “myocardial strain” (or simply “strain”) as used here refers to deformation (e.g., shortening, thickening and/or lengthening) of the myocardium. As is generally known in the art, myocardial strain is a measure of regional left ventricle function.
There are many conventional ways to measure strain using MR images. The most popular approach uses a special pulse sequence to create a dark grid (tags) in the myocardium that deforms with the myocardium. Tags are tracked during the cardiac cycle and strain can be calculated. However, tagged MR generally results in poor spatial resolution. Another technique, displacement encoding with stimulated echoes (DENSE), directly measures a 3D displacement at every pixel in the image, but the acquisition time is very slow. Other conventional techniques such as strain encoding (SENC) offer faster acquisition time but are limited to through plan strain.